Process for producing a replica of a surface



y 1950 E. s. MACHLIN ETAL 2,514,403

PROCESS FOR PRODUCING A REPLICA OF A SURFACE Filed May 15, 1945 2Shee'ts-Sheet 1 y 1950 E. s; MACHLIN ETAL 2,514,403

PROCESS FOR PRODUCING A REPLICA OF A SURFACE Filed May 15, 1945 2Sheets-Sheet 2 its backings.

Patented July 11, 1950 PATENT OFFICE I OF A SURFACE PRocEss FORPRODUCING A REPLICA.

Eugene S. Machlin, Cleveland Heights, and Louis L. Ornstein, EastCleveland, Ohio Application May 15, 1945, SerialNo. 593,897

2 Claims. (CI. 3550) (Granted under the act of March 3, 1883, as 1amended April 30, 1928; 370 0. G. 757) The invention pertains to thereplica r reproduction of the characteristics of a surface on anon-metallic film, said non-metallic replica film being preserved forexamination, and to the process of producing and using the replica film.

Many items have been made in the past to obtain a measure of the surfacefinish of machine finished surfaces. Such methods have made use ofexpensive instruments which are not available for wide distributionbecause of their high cost. Other less expensive methods have been usedto reproduce surfaces of specimens in the field. of scientific research.These latter methods make-use of replicas of the surfaces which are tobe reproduced.

It is an object of this invention to make use of the replica type ofreproduction process in a unique fashion which enables very quickdeterminations of the character or surface finish of a surface to beobtained.

A further object of this invention is to provide a method for obtainingthe surface finish or measure of surface character of internal surfaces.For example, where a measure of the area of indentation of a surface idesired, ordinary tracer-type surface finish measuring instruments willnot measure this area. However, the use of the replica reproductionprocess in conjunction with a standard comparison according to thepresent invention will enable these areas of indentation to be measured.Machines now available for measuring internal indentation areasare verycostly and hence limited in use. The replica reproduction processaccording to the present invention offers an inexpensive, easy method ofobtaining internal indentation area measurements.

A further object is to provide an inspection surface finish control bymeans of, for example, replica reproduction comparison measurements orother measurements.

Other objects and features of the invention will be apparent from thefollowing description taken in conjunction with the accompanyingdrawings which are exemplary and in which:

. Fig. 1 is an exploded view of the elements of the article and showingthe elements employed in the process of producing the replica.

Fig. 1a is a view of the prepared replica blank and its backing,

Fig. 2 is a View showing the parts in place after the solvent has beenapplied and ready for the application of pressure.

Fig. 3 is a view of the completed replica with Fig. 4 is a plan view ofthe same.

Fig. 5 is a view of a comparison apparatus.

The surface replica and process of the present invention has been foundparticularly advantageous for measuring the porosity of chromium platedsurfaces, while not being limited thereto.

One of the mostpromising cylinder-bearing surfaces for piston ringsoperating in an aircraft engine at high power outputs is porous chromiumplate. The chief difficulty in the use of chromium plating has been thatsome porous chromium-plated cylinders wore exceptionally well whereasothers wore exceptionally poorly. Because of the uncertainty of theresults chromium plating has not been generally adopted for cylinders ofhigh-power engines. The reason for the difference in operation betweentwo cylinders that are chromium plated by the same method may lie inthe-type anddegree of porosity.

The lack of adequate methods of inspecting and specifying the optimumporosity of chromium-plated surfaces has greatly retarded progress inthe used porous chromium plate. For

this reason a satisfactory method of measuring the'porosity of porouschromium-plated surfaces has been sought. Such instruments as the Brushsurface analyzer, the Profilometer, and a lightreflection meter havebeen used with little success,

The process of the present invention-is simple, fast and sufficientlyaccurate to specify porosity of chromium-plated cylinders for aircraftengine tests. It is particularly suited for shop use as a means ofinspection prior to engine operation.

The blank I' for the replica may desirably be prepared by brushing,spraying, dipping, pouririg or otherwise applying a liquid non-metallicsubstance such as stripping lacquer or plastic material in a thin filmon a smooth, preferably very highly polished surface, the roughness ofwhich is less than 3 microinches, R. M. S. After the film has dried onthe smooth surface, it is stripped or peeled therefrom, and may be cutinto strips or pieces of the desired size. Other methods may be used toprepare the blank film i, such as rolling a plastic or lacquer film orpressing said film, so long as the surfaces of the film are not marredby the surfaces of the rolls or press.

In the embodiment shown in the drawing, I represents the nonmetallicprepared film; 2 is the surface which is being reproduced; 3 is thesolvent applied in any suitable way which is either placed on 2 or onthe under side 4 of I; 5 is a backing for I having an adhesive layer onits under side '6. There is an opening I in the backing 5 through whichpressure is applied by means of pad 8 which preferably is not soluble insolvent 3.

The film I may desirably be provided with the backing 5 of suitablematerial, such as paper or cardboard or other flexible material, havingan opening therein, desirably such as indicated at I. The backing 5 ispreferably provided on its side 6 with adhesive by means of which theside 6 of backing 5 is secured to the blank film I, as indicated in Fig.1a. A supply of blanks for replicas may be prepared and stored forfuture use, if desired.

In obtaining a replica reproduction of the surface 2, solvent 3 for thefilm I is applied by spraying or otherwise, either on the surface 2 oron the side 4 of film I. A thin film of solvent is desirable.Immediately, or a few seconds after the solvent has been applied, theside 4 of the film I is pressed into intimate contact with the surface 2desirably by hand pressure applied against the protecting pad 8, andthrough the opening I in backing 5. Fig. 2 shows the parts in placeafter the solvent has been applied, ready for pressure to be applied tothe pad 8. Pressure is maintained for a short time, preferably not lessthan 15 seconds and not more than 1 minute. During the maintenance ofpressure the film becomes dried in contact with the surface to be reproduced.

After the pressure and drying interval has been completed, the replicafilm I is gently peeled or stripped from the surface 2. It is thenprovided with a suitable mounting or backing means which may desirablycomprise a backing such as indicated at It! having an adhesive side 9 tobe attached to the replica film with the opening II in the backing Imatching or registering with the opening I of the backing 5. This isshown in Figs. 3 and 4, in which I is the non-metallic replica film; 5and I8 are the preferably fiexible backings for the film I; B and 9 arethe adhesive sides of the backings 5 and ID; and I and !I represent theopenings in the backings 5 and Ill.

The replica, as seen in Figs. 3 and 4, is then ready for viewing andexamination, for example, by a standard comparison method or othersurface finish measurements.

In order to measure porosity or examine the replica film; a magnifiedimage of the replica may desirably be projected onto the screen of afilm viewer, such as a 35 millimeter film viewer, as indicated in Fig.5.

In Fig. 5, the film viewer or projection apparatus is indicated at I2. 1A strip, desirably consisting of a number of standard replicas of knownporosities or surface configuration, sandwiched between two strips ofcelluloid is mounted in place in the film viewer or projection apparatusl2, as indicated at I3. The standard or known replicas preferably havebeen accurately calibrated for percentage porosity by measuring the areaof the pores. A strip in which is placed the sample replica whosesurface finish or surface character is being compared to standardreplica strip I3, is indicated at I4.

The projections of the standard and unknown porosity surface replicasare indicated at I5 and I6, respectively. To obtain a comparison, thesample unknown replica I4 is placed in the projection or viewingapparatus l2, so that its projection appears at l6 next to theprojection of the standard replica l3 which appears at l5. Any knownreplica image can be quickly obtained by shifting the standard replicastrip. The unknown porosity is obtained by matching the sample replicaimage to one of the known replica images.

The comparison method enables an untrained operator, to choose orbracket the limits of the unknown porosity or the percentage area ofsurface identation to nominal surface area, to within approximately 5percent of the area of surface indentation of the sample replica.

An important feature of the method of the present invention is theaction of the solvent 3 to soften the side 4 of film I so that the filmI being placed in intimate contact with surface 2, the softened side 4will conform to the asperities and hollows existing in the surface 2.Such conformity will become permanent as the softened side 4 of film Ihardens and sets. Such an action and method provides for a very quickmeasurement of surface finish or surface indentation area to beobtained.

The surface porosity of a chromium-plated cylinder can be identified bythe process of the present invention as to type and measured as to valuein approximately one minute.

The replica method is suitable for use in machine shops and platingplants where a quick check of the type or the quality of the porosity ofchromium-plating or other surfaces is required. The apparatus is simpleand inexpensive. Inexperienced personnel can be trained to measureporosity in a relatively short time. Approximately two minutes arerequired for a complete measurement, the first minute being required tomake the replica and the second minute to match the unknown porosity.

As a film material, it has been found that Ault and Wiborg Protektol No.28 is particularly suitable. This material is easily stripped from thehighly polished surface in forming the replica 'blank without marringthe surfaces of the film in any way.

Materials other than the stripping lacquer or liquid plastic may be usedin this method, with suitable solvents therefor.

A suitable solvent for the Protektol N0. 28 is Ault and Wibor No. 2069,Protektol Reducer.

If this method were used in a honing shop, removal of the cylinder fromthe honing machine would be unnecessary. The surface to be checked, maybe cleaned, the replica taken, the porosity measured, and honingcontinued or stopped, depending upon what results showed.

Any standard film viewer that is inexpensive or readily portable may beused in the process, and

-' should preferably be installed in a darkened room.

It may be desirable to have the film of known replicas wound on a spoolso that the known samples can be moved across the field of view with aminimum of difiiculty. The viewer may preferably be provided withreversible motor driven shafts. Both samples are subjected in the viewerto the same lighting conditions and are shown side by side to facilitatecomparison. A magnification of 16 may desirably be employed.Magnifications as high as 50, however, are available with stockequipment. Lower magnification has the advantage that a larger area canbe examined and a more representative sample of porosity can thus beobtained. Samples of both channeled and normal types of porosity havebeen examined and are readily distinguishable. Thus, type of porosity aswell as percentage porosity can be obtained by this method.

It will be understood that various changes in the construction andarrangement of parts and in the process may be made without departingfrom the spirit of the invention and it is not intended to limit theinvention other than by the terms of the appended claims.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

What is claimed is:

1. Steps in a method of obtaining a replica or reproduction of a surfacecomprising applying a backing having an opening therein to a strip ofnon-metallic film by means of adhesive to act as a protection againstdamage and for ease in handling, applying the unbacked side of said filmto a surface, the features of which it is desired to reproduce, with theapplication of liquid solvent for said film, applying pressure to alocalized portion of said film through said opening in the backing,allowing the film to dry in pressure contact with said surface, removingthe film from said surface, adhesively applying a protecting backinghaving an opening therein to the unbacked side of said film with theopening substantially registering with the opening in the backing firstmentioned, and exposing the replica on the said localized portion of thefilm which is formed in that part of the film bounded by the edges ofthe openings in the backings.

2. Steps in a method of obtaining a replica or reproduction of a surfacecomprising applying a backing having an opening therein to a strip ofnon-metallic film by means of adhesive to act as a protection againstdamage and for ease in handling, applying the unbacked side of said filmto a surface, the features of which it is desired to reproduce, with theapplication of liquid solvent for said film, applying a protecting padto said backing overlying the opening therein, applying pressure to alocalized portion of said film through said opening in the backing bypressing on said protecting pad, allowing the film to dry in pressurecontact with said surface, removing the film from said surf-ace,adhesively applying a protecting backing having an opening therein tothe unbacked side of said film with the opening substantiallyregistering with the opening in the backing first mentioned and therebyexposing the replica on the said localized portion of the film which isformed inthat part of the film bounded by the edges of the openings inthe backings.

EUGENE S. MACI-ILIN.

LOUIS L. ORNSTEIN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 241,005 Hart May 3, 1881 573,928Stevens Dec. 28, 1896 934,214 Ratignier Sept. 14, 1909 1,028,296 SohierJune 14, 1912 1,146,855 Emerson July 20, 1915 1,387,488 Holmer Aug. 16,1921 1,467,108 Hodgson Sept. 4, 1927 1,811,971 Sauer June 30, 19312,046,566 Lucas July 7, 1936 2,070,023 Olsen Feb. 9, 1937 2,074,704Osborn Mar. 23, 1937 2,090,914 Porter Aug. 24, 1937 2,113,166 ZinserApr. 5, 1938 2,116,536 McKee May 10, 1938 2,119,577 Gray June 7, 19382,184,672 Jackman Dec. 26, 1939 2,202,683 Baesgen May 28, 1940 2,243,674Koch May 27, 1941 2,291,173 Simpson July 28, 1942 2,296,804 Winnek Sept.22, 1942 FOREIGN PATENTS Number Country Date 4,874 GreatBritain 1880 54,by J. A. Broadston, Surface Checking Gage 00., Hollywood, California.

